1. Field of the Invention:
This invention relates in general to electrical submersible pumps and in particular to an electrical submersible pump that is suspended on conductor cable.
2. Description of the Prior Art:
Large electrical submersible pumps are commonly used to pump wells that are of considerable depth and which require large flow rates. The pump will have a submersible three-phase alternating current (AC) electrical motor. The pump will be of a centrifugal type, having a large number of stages. The pump is lowered on tubing into the cased well or into a liner within the cased well. Power to the motor will be supplied from the surface over a three-phase cable having three conductors. The formation fluid will be pumped through the tubing to the surface.
Periodically, the downhole pumping assembly must be pulled to the surface for maintenance. A workover rig will be needed to pull the tubing and pump assembly from the well. The tubing typically comprises steel pipe sections screwed together. Pulling a pump is time-consuming and expensive. It is particularly a problem for remote wells and offshore wells where the availability of pulling rigs is limited.
Suspending the pumping assembly on a cable has been proposed. In such a case, the pump pumps the formation fluid through the casing or liner to the surface. For maintenance, the pump can be retrieved by a winch which will winch the cable up, eliminating the need for a workover rig.
Cable suspended systems proposed in the past require a specially constructed cable because the conventional three-phase power cable lacks sufficient tensile strength to support the weight of the pump assembly. The cable proposed in the past has structural supporting members, as well as three conductors. Some of the cables proposed had major technical difficulties because of the complexity of the cable construction, difficulty in splicing, and the tendency of the cable to rupture under gas depressurization. Early efforts resulted in failures and abandonment. More recent suspended cables proposed have an even more complex cable utilizing molded vertebrate While this may be feasible, the cost of the cable will be high.